1. Field of the Invention
The present invention relates to a wheel angular acceleration sensor for an anti-lock controller for vehicles and pariticularly, to an improvement of a wheel angular accleration sensor comprising a flywheel rotatably and axially displaceably mounted on an output shaft rotatable in operative connection with a wheel which is braked by a wheel brake; a clutch adapted to transmit a driving torque of the output shaft to the flywheel under a normal operating condition and, when the wheel is about to become locked during braking, to permit overrunning of the flywheel; and a cam mechanism operable in response to the overrunning of the flywheel to provide an axial displacement to the flywheel, the clutch and the cam mechanism being interposed in series between the output shaft and the flywheel, and the axial displacement of the flywheel being output as a control signal for a braking force of the wheel brake.
2. Description of the Prior Art
In such conventional wheel angular acceleration sensor, the cam mechanism comprises a drive cam plate fixedly mounted on the output shaft, and a follower cam plate which is engaged with the drive cam plate and produces an axial displacement as it rotates relatively to the drive cam plate, and a clutch is interposed between the follower cam plate and the flywheel to spring-bias the flywheel toward the drive cam plate (see Japanese Patent Application Laid-open No. 128253/81).
With the above conventional arrangement, if a friction surface of the clutch is worn, the flywheel spring-biased toward the drive cam plate is obliged to axially displace by an amount corresponding to such wearing and hence, the original axial position of the flywheel cannot be stabilized. For this reason, even though the flywheel is axially displaced due to the overrunning thereof, a slight error can be made in the timing at which the axial displacement is picked up as a control signal for the braking force.